MOSCOW (AP) — Warplanes from the U.S.-led coalition operating over Syrian government-controlled areas west of the Euphrates River will be tracked as potential targets, Russia’s Defense Ministry said Monday, a day after the U.S. military shot down a Syrian air force jet. Moscow condemned the downing of the Syrian jet after it dropped bombs near the U.S.-backed Syrian Democratic Forces that are fighting the Islamic State group in Syria’s increasingly complicated civil war.

The downing of the warplane — the first time in the conflict that the U.S. has shot down a Syrian jet — came as Iran fired several ballistic missiles at IS positions in eastern Syria in retaliation for two attacks by the extremists in Tehran earlier this month that killed 17 people.

Areas of northern Syria west of the Euphrates were controlled by IS before Syrian government forces captured most of them in recent months. The Russians appear to want to avoid further U.S. targeting of Syrian warplanes or ground troops that have come under U.S. attack in eastern Syria recently.

Moscow also called on the U.S. military to provide a full accounting of why it decided to shoot down the Syrian Su-22.

Russia, a key ally of Syrian President Bashar Assad, has been providing an air cover to the government’s offensive since 2015.

But in April, Russia briefly suspended a hotline intended to prevent midair incidents with the U.S. over Syria after the American military fired 59 missiles at a Syrian air base following a chemical weapons attack that Washington blamed on the Assad government.

The U.S. military confirmed that one of its F-18 Super Hornets shot down a Syrian Su-22 that had dropped bombs near the U.S. partner forces SDF. Those forces, which are aligned with the U.S. in the campaign against the Islamic State group, warned Syrian government troops to stop their attacks or face retaliation.

In comments to Russian news agencies, Russian Deputy Foreign Minister Sergei Ryabkov compared the downing to “helping the terrorists that the U.S. is fighting against.”

“What is this, if not an act of aggression?” he asked.

Viktor Ozerov, chairman of the defense and security committee at the upper chamber of Russian parliament, described the Defense Ministry’s statement as a warning.

“I’m sure that because of this neither the U.S. nor anyone else will take any actions to threaten our aircraft,” he told state-owned RIA Novosti news agency. “That’s why there’s no threat of direct confrontation between Russia and American aircraft.”

Ozerov insisted that Russia will be tracking the coalition’s jets, not shooting them down, but he added that “a threat for those jets may appear only if they take action that pose a threat to Russian aircraft.”

Meanwhile, the U.S.-backed opposition fighters said Assad’s forces have been attacking them in the northern province of Raqqa and warned that if such attacks continue, the fighters will take action.

Clashes between Syrian troops and the SDF would escalate tensions and open a new front line in the many complex battlefields of the civil war, now in its seventh year. Clashes between the Kurdish-led SDF and Syrian forces have been rare and some rebel groups have even accused them of coordinating on the battlefield.

The clashes come as both sides are battling the Islamic State group, with SDF fighters now focusing on their march into the northern city of Raqqa, which the extremist group has declared to be its capital.

Government forces have also been attacking IS in northern, central and southern Syria, seizing 25,000 square kilometers (9,600 square miles) and reaching the Iraqi border for the first time in years.

SDF spokesman Talal Sillo said the government wants to thwart the SDF offensive to capture Raqqa. He said government forces began attacking SDF on Saturday, using warplanes, artillery and tanks in areas that SDF had liberated from IS.

Sillo also warned that if “the regime continues in its offensive against our positions in Raqqa province, this will force us to retaliate with force.”

The Britain-based Syrian Observatory for Human Rights, which tracks Syria’s war, said government forces expanded their presence in Raqqa province by capturing from IS the town of Rasafa.

Iran’s launch of its ballistic missiles against IS hit Syria’s eastern city of Deir el-Zour on Sunday night and was its first such strike in the conflict. Previously, it has been providing crucial support to Assad’s forces.

Iran’s powerful Revolutionary Guard said it launched six Zolfaghar ballistic missiles from the western provinces of Kermanshah and Kurdistan. Video on Iranian state TV showed the weapons on truck missile launchers in the daylight before the nighttime volley.

The missiles flew over Iraq before striking what the Guard called an IS command center and suicide car bomb operation in Deir el-Zour, over 600 kilometers (370 miles) away. The extremists have been trying to fortify their positions in the Syrian city in the face of a coalition onslaught on Raqqa.

Syrian opposition activist Omar Abu Laila said two Iranian missiles fell in and near the eastern town of Mayadeen, an IS stronghold. There were casualties, said Abu Laila, who is originally from Deir el-Zour and currently lives in Germany, where he runs a website about the province.

The Islamic State group did not immediately acknowledge the attack. Iraqi lawmaker Abdul-Bari Zebari said his country agreed to the missile overflight after coordination with Iran, Russia and Syria.

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